Electric instantaneous water heater



April 19, 1966 w, FELD ELECTRIC INSTANTANEOIJS WATER HEATER 4 Sheets-Sheet 1 Filed Jan. 31, 1961 Fig.1

Fig.3

April 19, 1966 w. FELD 3,247,359

ELECTRIC INSTANTANEOUS WATER HEATER Filed Jan. 31, 1961 4 Sheets-Sheet 2 April 19, 1966 w. FELD 3,

ELECTRIC INSTANTANEOUS WATER HEATER Filed Jan. 31, 1961 4 ShQE'GS- -ShGGt 5 April 19, 1966 w. FEL'D 3,247,359

ELECTRIC INSTANTANEOUS WATER HEATER I Filed Jan. 51, 1961 4 Sheets-Sheet 4 14 I I :13 I49 I I I I I United States Patent ELECTRIC INSTANTANEOUS WATER HEATER Walter Feld, Traunstein, Upper Bavaria, Germany, as-

signor to Siemens=Electrogerate Aktiengesellschaft,

Munich, Germany, a corporation of Germany Filed Jan. 31, 1961, Ser. No. 86,096) Claims priority, application Germany, Feb. 10, 1960, S 67,035; Dec. 2, H60, S 71,514 6 Claims. (Cl. 219- 503) My invention relates to electric water heaters of the instantaneous type.

Since in such heaters the water must reach the desired temperature while flowing through the apparatus, it is necessary to provide for a particularly good heat contact between the electric heater and the water. It is further necessary to prevent the water from assuming an electrical potential other than ground or zero potential.

In one known electric water heater of the instantaneous type, the electric heaters consists of bare windings located in tubes of plastic which are traversed by the water to be heated. If in such a heater the water supply ceases and the electric control switch fails, for example by sticking of its contacts, the heater windings reach incandescent temperature and may then embed themselves into the plastic material which causes damage to the apparatus and may ignite the plastic.

Such trouble is avoided in another known electric water heater of the instantaneous type that comprises an insulat ing body with tubular openings into which a number of tubes of heat and arc-resistant ceramic material are inserted, the electric heater windings proper being located within the ceramic tubes and the water passing through the tubes and along the windings.

It is an object of my invention to secure an efiicient instantaneous water-heating performance without any electrical danger to the user by a simpler and more troublefree apparatus than heretofore available.

To this end, and in accordance with a feature of the invention, the water heater is provided with helical heater windings which consist of tubular electric heating elements and are joined together along adjacent turns of the helix so as to constitute a single elongated tube whose metallic surface, to be contacted by the water to be heated, is insulated from the internal heater wire proper and is connected to electrical zero potential when the apparatus is in operation.

According to a more specific feature of my invention, the helical turns of the tubular electric heater body are soldered, welded or otherwise directly joined with each other so as to require no other tubular structure to form a tube. If desired, individual openings may be left between the helical turns thus joined together.

According to another, preferred feature of my invention however, the tube structure of the water heater, to be traversed by the water to be heated in a single pass, consists of a metal tube upon which the turns of the helical heater winding are concentrically mounted. According to a feature more specific than the one just mentioned, the inner metal tube is provided with lateral openings. This is particularly advantageous if the mutually joined turns of the heater winding proper are also provided with individual lateral openings.

For securing a particularly good heat contactbetween the metal tube and the water flowing therethrough, the inner side of the tube is preferably provided with grooves. These grooves may be given helical shape to impart to the water a helical motion, thereby further improving the heat transfer from the metal tube to the water. The outer side of the metal tube may also be provided with helical grooves to form a seat for the turn of the tubular ICC electric heater windings which are preferably soldered or welded to the tube.

According to still another feature of my invention, the tube formed by the electric heater windings themselves is eneveloped by a jacket tube of metal, thus providing an annular interspace. Such a a water heater can be so designed that the flow of water to be heated passes along the inner space of the helical heater windings as well as along the outside thereof.

According to a further feautre of my invention, relating to three-phase electric energization of the water heater, three helical windings of tubular electric heaters are provided for the respective three phases. This can be done, for example, by arranging the three windings for multi-phase operation in form of a multiple-turn helix. However, other designs of a water heater according to the invention are also suitable for multi-phase operation.

For example, a separate tube structure may be formed of the heater windings for each phase, and these tubes may be traversed by water in parallel or series relation to each other.

According to another feature of my invention, the tube formed of the electric heater windings is provided, at least at one end, with a screw thread, for example an external thread, in order to facilitate connecting the helical structure to the water supply line. It is often preferable to provide such screw threads on an end portion of the tubular structure that has a smaller cross section than the main portion traversed by the water.

The outer surface of the water heater is preferably given a low degree of heat radiation, for example by coating it with aluminum varnish, or by giving it a good reflective surface, or also by enclosing the outer surface of the heater with heat insulating material.

The water heater is further preferably provided with a protective temperature-limiting device whose heat sensor is mounted on the tubular heater windings.

The'foregoing and more specific objects, advantages and features of my invention, said features being set forth with particularity in the claims annexed hereto, will be apparent from, and will be described in, the following with reference to the embodiments of water heaters according to my invention illustrated by way of example on the accompanying drawings, in which:

. FIG. 1 is a front view of a water-heater tube formed by mutually adjacent, helical turns of a tubular electric heater.

FIG. 2 shows a section of part of a water heater de signed for three-phase operation, the tubular heater turns being mounted on a metal tube with grooves on its inner and outer surfaces.

FIG; 3 shows an end portion of a water heater according to FIG. 2 and also illustrates a protective temperature limiting device.

FIG. 4 is a partly sectional view of another instantaneous water heater.

. ductor 1 is wound to a helical coil with the individual turns closely adjacent to each other. The turns jointly form a tube whose interior is to be traversed by the water to be heated. If desired, the water may also flow on the outside along the tubular structure which for this purpose is to be enclosed in a jacket (not shown). In this manner,

the inner as well as the outer surface of the tubular structure may be used for imparting heat to the water. A The tubular structure may directly form a tube with a completely sealed tubular Wall, by having the adjacent turns of the helical winding soldered or welded together to form an integral body.

The heating conductor 1 in all illustrated embodiments consists of a heating wire, preferably coiled as a thin helix, which is embedded in ceramic insulating powder and enclosed by an outer tube of metal, such as steel. Such heating conductors are known as such and are generally used, for example, in electric ranges and hot plates.

FIG. 2 shows in section a portion of a modified heater structure designed for three-phase electric energization of the heating conductors. The heater coil is wound of three groups of turns 2, 3 and 4 whose respective heating conductors 2a, 3a, 4a are to be connected to the three phases of the current-supply line. As mentioned, the conductors, such as the conductor 2a, may constitute a narrow helix and an embedded in ceramic insulation 2b and sheathed by a metal tube 20. The turns are mounted on a metal tube 5 and are joined therewith by soldering or welding. The metal tube 5, consisting for example of copper, has interior helical grooves so that the water flowing through the tube is caused to travel in rotary, helical motion. The outer surface of tube 5 is likewise provided with helical grooves which constitute a triple helical line and in which the heater windings 2, 3, 4 are seated.

The invention further contemplates a tubular metal gether to form an axially elongated tubular conduit and connecting therewith pipes which communicate with the conduit for passing water to be heated. Moreover, the invention contemplates (as an alternate embodiment) the so-formed conduit possessing lateral openings between the adjacent turns. Where the tube 5 is used, the invention contemplates (as an alternative) both the winding forming between each other lateral openings and the tube possessing lateral openings registering with the openings in the windings.

The invention further contemplates a tubular metal jacket coaxially surrounding the winding turns and forming an annular interspace together with the so-formed conduit, with the pipe means communicating also with said interspace to pass Water therethrough.

According to FIG. 3, the inner tube 5 is upwardly extended beyond the heater windings and possesses a portion 6 of smaller diameter with an external screw thread. The thread 7 serves for connecting the heater to a Water supply pipe. Also shown in FIG. 3 is a portion of a heatresponsive sensor 8 which is soldered onto the three windings 2, 3 and 4 and forms part of a thermostatic safety switch for limiting the temperature.

Due to the fact that the outer metal enclosure of the electric heater windings, such as the enclosure denoted by 4a in FIG. 2, are in electric contact with the inner metal tube 5 which in turn is connected to a water supply pipe, the metallic outer enclosures of all winding turns are reliably kept on electric zero potential by grounding.

According to another feature of my invention, the heat transfer from the electric heater to the water passing therethrough can be further improved by enforcing a turbulent flow of the water within the tubular portion of the water heater, either by securing a sufliciently travelling speed of the water and/ or by providing additional means for causing a whirling motion of the water.

For this purpose, and in accordance with a more specific feature of my invention, it is preferable to subdivide the heat-exchanger space within the tubular structure of the heater by labyrinth-forming inserts. A particularly favorable design of such an insert consists of a singleturn or multiple-turn helical structure whose surface has stepped or wavy shape.

In a preferred embodiment of my invention, I provide the apparatus with a central pipe which not only serves for supplying or discharging the water but which also forms a support or guide for a helical insert of the type just mentioned. By virtue of these features, the flow cross sections within the labyrinth portion of the apparatus are not larger than the flow cross sections at the inlet and outlet locations. This secures a good whirling of the water and there-by improves the heat exchange from the electric heater to the Water.

Embodiments of the type just mentioned are illustrated in FIGS. 4 through 9.

The instantaneous water heater shown in FIG. 4 is provided with a Water outlet pipe 11 and a water supply pipe 12 coaxially aligned with each other. The two pipes communicate with each other through a tubular jacket 13. The jacket carries a helical electric heater 14 of the tubular type described above. The turns of the heater coil are immediately adjacent to each other and are joined with the jacket 13 by soldering. Located in the tubular jacket 13 is an insert 15 of sheet metal such as copper. The insert greatly lengthens the travel path of the water from the inlet to the outlet pipe in the sense described in the foregoing. The surface of the helical structure 15 is preferably given a stepped or wavy configuration.

The water heater shown in FIG. 5 is designed to cause a reversal in water-flow direction within the heater for improved heat exchange. The water enters the apparatus at inlet 11 and through a central pipe 16, extending upwardly along the axis of a copper jacket 13 and of the tubular structure formed by the turns of the electric heater coil 14. The heated water leaves the apparatus through a lateral pipe 12 communicating with the interior of the jacket 13. A helical guiding structure 15 is mounted on the central pipe 16 and is also in good heat conducting contact with the jacket 13. The jacket 13 is closed by a cover 17 at the top and by a plate 18 at the bottom.

Since the tubular electrical heating conductors are mounted on the jacket outside, and by virtue of the fact that a suitable flow velocity and whirling of the water is secured by the above-described inserts, the over-all length of the water heater can be made shorter than heretofore required. As a result, a reduction down to approximately one-third of the water volume required can be obtained in comparison with known electric instantaneous heaters. For example, satisfactory instantaneous heaters according to the invention have been produced whose water volume amounted only to about 0.3 liter. For the same reasons, the over-all length of the tubular electric heater can be reduced to approximately one-half of the one heretofore necessary for an otherwise similar performance. Due to the heat capacity, the reliability of of the apparatus is improved since the temperature-responsive safety switches respond more rapidly. A water heater of this type furnishes hot water practically immediately upon opening the faucet and operates with a better efiiciency than the heaters heretofore known.

A complete heating apparatus embodying the abovementioned and further features of the invention, will be described presently with reference to FIGS. 6 to 9. This apparatus is designed to immediately furnish hot water at a location where space is at a premium. The apparatus comprises a vertical base plate or mounting panel 19 to which the water heater unit 20 is fastened by means .of brackets 21, 22, 23. A water supply pipe 24 is connected to a pressure or flow-responsive gauge 25 of conventional design available in the trade. The gauge has a tappet 26 for operating an electric snap switch 27 which may have one or more contacts depending upon whether the electric heating conductors are connected in single-phase or multi-phase relation to the electric utility line. The embodiment shown in FIG. 7 is adapted for use with a threephase electric utility line system. The heater coil is formed of three adjacent windings 14, each terminating in a hook-shaped connector as shown at the top of FIG. 7. An intermediate pipe (FIG. 6) connects the gauge 25 with the inlet pipe 11 of the heating unit proper. The gauge 25 is fastened to the mounting panel 19 by a bracket 35.

The design and operation of the heating unit 20 corresponds to the one described above with reference to FIG. 5.

The apparatus further comprises a pilot lamp 28 and a fuse-type limit switch 29 which is fastened to the mounting panel 19 by means of an angle piece 30 (FIG. 8). The switch 29 is a known component available in the trade. It comprises a shaft 31 normally biased for rotation about its axis by means of a tensioned spring (not shown) within the switch housing. The shaft 31 is locked in spring-tensioning rotary position by means of a solder fuse 32 (FIGS. 7, 8) which is formed by a bracket 33 mounted on the heater unit 20 and by a bridge piece 34, both of them joined with the shaft 31 by means of solder. When the heater temperature becomes excessive, the solder melts and the switch 29 opens (FIG. 9). As shown further diagrammatically in FIG. 9, for operation with a three-phase current supply system, the three windings 14 of the heater coil are individually connected in series with the fuse-type limit switch 29, the electric snap switch 27 and a respective line of the three-phase supply system.

The mounting panel 19 has an opening 47 (FIG. 6) for the passage of an electric cable. When in operative condition, the mounting panel 19 is fastened by bolts 36 (FIGS. 6, 7) to a supporting wall. After mounting the panel 19, a cover 49 is placed upon the mounting panel 19 and is fastened thereto by bolts at 37.

The apparatus is provided with a mixer valve 43 whose inlet nipple 42 is connected to a cold water supply pipe when the apparatus is in operative condition. The mixer valve has two nipples 40 and 41 for hot water and cold water respectively. The two nipples are joined by respective cap nuts 38 and 39 with the hot water outlet pipe 48 and the cold-water inlet pipe 24 of the apparatus. The mixer valve has a hot-water faucet 44 and a coldwater faucet 45. The hot, mixed, or cold Water leaves the mixer valve through its outlet pipe or nipple 46.

When the hot-water faucet 34 is turned open, the flowresponsive gauge 25 closes its switch 27 and thereby connects the electric heating conductor 4 to the current supply line N (FIG. 9). Due to the small thermal capacity of the apparatus, the water dispensed from the apparatus is immediately heated to a temperature between 65 C. and 38 0, depending upon the quantity of water drawn per unit of time. The temperature of 65 C. corresponds to a withdrawal of 5 liters per minute, and the temperature of 38 C. to liters per minute. By opening the coldwater faucet 45, any quantity of cold water can be withdrawn or can be adrrrixed' to the hot water. When closing the hot-water faucet 34, the electric heating conductor 4 is disconnected from the current supply line by opening of theswitch 27. The switch 27 is electrically connected in series with the fuse-operated temperature limit switch 29 which disconnects the heating conductor 4 from the current supply if the main switch 27 fails to disconnect the heater unit 20, for example due to trouble at the flow-responsive switch 25.

The above-described apparatus according to FIGS. 6 to 9 can be given a volume smaller than 3.6 liters while affording the above-described satisfactory operation.

The invention also contemplates heat radiation reducing means on the outer surface of the electric water heater in FIG. 2.

It will be obvious to those skilled in the art, upon studying this disclosure, that with respect to details .an instan'taneous water heater according to my invention can be modified in various respects and hence may be given embodiments other than particularly illustrated and described herein, without departing from the essential features of my invention and within the scope of the claims annexed hereto.

I claim:

1. An electric instantaneous water heater comprising an elongated thin-walled metal tube having a closed and an open end, electric heater means comprising at least one helical coil coaxially mounted on the exterior of said metal tube and having a heater Wire and a tubular metal sheath enclosing said Wire and insulated therefrom, said coil having its turns located immediately adjacent to each other and metallically bonded with said tube, a helical guide structure mounted in said tube in coaxial relation thereto and forming a helical water-flow path from said closed end to said open end of said tube, pipe means comprising a pipe coaxial with said guide structure and extending axially within said tube, said pipe being open at both ends thereof for the flow of water therethrough, water inlet means communicating with the open end of said pipe at said open end of said tube, water outlet means communicating with said flow path at said open end of said tube, the end of said pipe at the closed end of said tube being spaced from said closed end and communicating with said fiow path at said closed end for passing water therethrough from said water inlet means, said guide structure having a generally wavy surface configuration along said path and being located between said pipe and said tube and in contact with both, electric current supply means connected with said heater wire, and a Water mixer assembly operatively associated with said water inlet and outlet means for selectively mixing heated and unheated water.

2. In an electric Water heater according to claim 1, said electric supply means comprising a multi-phase circuit, said heater means having a plurality of respectively different helical coils of Winding turns whose heater wires are connected to respectively different phases of said circuit, said coils forming together a single multiple-tum helix with one turn of each phase adjacent to one turn of another phase of said circuit.

3. An electric water heater according to claim 1, in combination with a temperature-limiting switch means which forms part of said current supply means and has a temperature sensing memmber mounted in direct thermal contact with the heater.

4. In an electric water heater according to claim 1, said helical guide structure being water-tightly joined with at least one of said tube and pipe.

5. An apparatus as in claim 1, including current switch means connected with said current supply means, said inlet means being provided with Water pressure responsive means operatively connected between said current switch means and said pipe means for switching on power to said heater wire in response to water pressure in said pipe means.

6. An apparatus as in claim 1, said heater means having a plurality of coils, said electric current supply means having a plurality of phases each connected to a different one of said coils.

References Cited by the Examiner UNITED STATES PATENTS 1,270,198 6/1918 Parkhurst 219-301 X 1,746,522 2/1930 Carleton 219-307 2,369,526 2/ 1945 Brandi 219333- 2,775,683 12/1956 Kleist 218305 X 2,802,089 8/1957 Beck 219305 2,889,444 6/ 1959 Sliebel 219316- 3,005,888 10/1961 Putz 21939.41

FOREIGN PATENTS 220,834 2/1959 Australia.

285,034 9/ 1928 Great Britain.

310,321 8/ 1933 Italy.

253,430 11/1948 Switzerland.

RICHARD M. WOOD, Primary Examiner. ANTHONY BARTIS, MAX L. LEVY, Examinersu, 

1. AN ELECTRIC INSTANTANEOUS WATER HEATER COMPRISING AN ELONGATED THIN-WALLED METAL TUBE HAVING A CLOSED AND AN OPEN END, ELECTRIC HEATER MEANS COMPRISING AT LEAST ONE HELICAL COIL COAXIALLY MOUNTED ON THE EXTERIOR OF SAID METAL TUBE AND HAVING A HEATER WIRE AND A TUBULAR METAL SHEATH ENCLOSING SAID WIRE AND INSULATED THEREFROM, SAID COIL HAVING ITS TURNS LOCATED IMMEDIATELY ADJACENT TO EACH OTHER AND METALLICALLY BONDED WITH SAID TUBE, A HELICAL GUIDE STRUCTURE MOUNTED IN SAID TUBE IN COAXIAL RELATION THERETO AND FORMING A HELICAL WATER-FLOW PATH FROM SAID CLOSED END TO SAID OPEN END OF SAID TUBE, PIPE MEANS COMPRISING A PIPE COAXIAL WITH SAID GUIDE STRUCTURE AND EXTENDING AXIALLY WITHIN SAID TUBE, SAID PIPE BEING OPEN AT BOTH ENDS THEREOF FOR THE FLOW OF WATER THERETHROUGH, WATER INLET MEANS COMMUNICATING WITH THE OPEN END OF SAID PIPE AT SAID OPEN END OF SAID TUBE, WATER OUTLET MEANS COMMUNICATING WITH SAID FLOW PATH AT SAID OPEN END OF SAID TUBE, BEING SPACED FROM SAID PIPE AT THE CLOSED END OF SAID TUBE BEING SPACED FROM SAID CLOSED END AND COMMUNICATING WITH SAID FLOW PATH AT SAID CLOSED END FOR PASSING WATER THERTHROUGH FROM SAID WATER INLET MEANS, SAID GUIDE STRUCTURE HAVING A GENERALLY WAVY SURFACE CONFIGURATION ALONG SAID PATH AND BEING LOCATED BETWEEN SAID PIPE AND SAID TUBE AND IN CONTACT WITH BOTH, ELECTRIC CURRENT SUPPLY MEANS CONNECTED WITH SAID HEATER WIRE, AND A WATER MIXER ASSEMBLY OPERATIVELY ASSOCIATED WITH SAID WATER INLET AND OUTLET MEANS FOR SELECTIVELY MIXING HEATED AND UNHEATED WATER. 